Soda lime silica glass is widely used as a substrate glass for data storage medium such as a magnetic disk or an optical disk. However, a substrate made of soda lime silica glass was likely to undergo a so-called whitening phenomenon, whereby the surface state was likely to be substantially changed during its storage. Therefore, when such soda lime silica glass was used as a substrate for a magnetic disk, there was a problem such that a film such as an undercoating film, a magnetic film, a protective film or the like, formed on such a substrate was likely to be peeled. Further, in order to prevent such a whitening phenomenon, the soda lime silica glass may be subjected to chemical reinforcement treatment. However, such chemical reinforcement treatment increases a process step and brings about a problem such that stain is likely to remain on the surface of the substrate after the chemical reinforcement treatment. Under the circumstances, theretofore, a substrate glass for data storage medium has been proposed which is less susceptible to a whitening phenomenon and which is excellent in weather resistances even if no additional treatment such as chemical reinforcement treatment is applied (Patent Documents 1 and 2).
Patent Document 1: U.S. Pat. No. 6,949,485
Patent Document 2: U.S. Pat. No. 5,599,754